1. Field of the Invention
The present invention relates to an inverter apparatus and a method for using the inverter apparatus, particularly one where a heat sink is easily installed, removed, and changed.
2. Description of the Background Art
FIG. 7 shows the arrangement of a conventional inverter apparatus, wherein the numeral 70 indicates a heat sink, 71 denotes a power module secured to the heat sink 70 by screws 72 with a cooling surface 73 thereof on the bottom side, and 74 represents a printed circuit board which is disposed above the power module 71, connected electrically with the power module 71 by solder 75, and also fixed to the heat sink 70 by screws 76. 77 designates a cover which is secured to the heat sink 70 by screws 78 to protect the printed circuit board 74 from dust, dirt, foreign matter, impact and/or the like and to prevent the electric shock of a person who operates the inverter apparatus. 79 indicates a top of the cover 77, 80 designates a casing which accommodates the power module 71, and 81 denotes installation fittings of the heat sink 70.
The operation of the conventional inverter apparatus designed as described above will now be described. The printed circuit board 74 is loaded with the power circuit, control circuit, display unit, operation units, wiring, main circuit device drive and protection circuits, and other components to control, for example, the operation of an alternating-current motor. The power module 71 contains the respective main circuit devices of a converter circuit which converts an alternating-current input into a direct current and an inverter circuit which converts the direct current into an alternating current.
The power module 71 is connected electrically with the printed circuit board 74 by the solder 75, operates under the control of the signal of the drive circuit given as a result of the operations of the circuits on the printed circuit board 74, and switches the main circuit devices on/off to drive the alternating-current motor as desired. The heat sink 70 is secured in close contact with the cooling surface 73 of the power module 71 by the screws 76 and acts to dissipate heat generated by the main circuit devices contained in the power module 71 and thereby reduce the temperature below a specified value.
The conventional inverter apparatus arranged as described above has a first disadvantage involving excess cost. Specifically, the casing 80 of the power module 71 was further covered and protected by the cover 77. Accordingly, there was an added cost for the casing 80 of the power module 71.
The conventional inverter apparatus had a second disadvantage that it required the heat sink 70 to be quite large and have a high cooling capability, thereby increasing the size of the inverter apparatus. The large heat sink is required to serve the so-called high-frequency PWM control systems that have been preferred recently and have a high switching frequency (10 to 20 kHz) in order to reduce the electromagnetic noise generated by the alternating-current motor. However, such systems generate a great deal of heat due to the considerable heat loss of the main circuit devices in the inverter circuit contained in the power module 71, as compared to those in the conventional inverter circuit having the switching frequency of only several kHz.
Because of the low prices of rapidly switchable main circuit devices (such as IGBT's) and the increased speed of the microprocessor in the control circuit, there is only one significant basis for a difference in cost and size between the conventional inverters having the switching frequency of several kHz and the recently used high-frequency PWM control inverters having the high switching frequency of 10 to 20 kHz, namely, the heat sink. Hence, although slightly larger in size as compared to the conventional inverters having a switching frequency of only several kHz, inverters using high-frequency PWM which produces an effect on reducing electromagnetic noise are finding general use. However, there still is a desire to make the high-frequency PWM inverter apparatuses more compact.
Further, the conventional inverter apparatus had a third disadvantage based on its containment in a control box. The dimension in the depth direction of the heat sink, i.e., the height direction of the inverter apparatus shown in FIG. 7, must be increased because there is a predetermined size of installation space. Accordingly, the depth dimension inside the control box had to be increased and the control box could not be reduced in size.